1. Field of the Invention
This invention enables an existing optical disk apparatus to erase and write information on an optical disk in a single rotation with two optical heads loaded on one positioner.
2. Related Art
Recently, an optical disk apparatus, like a magnetic disk device, that can rewrite new information after erasing old information has appeared.
Such optical disk apparatuses that can erase/write (overwrite) are classified as either an external magnetic field type or a non-external magnetic field type. The non-external magnetic field type does not need an erasing action by an erase beam and can immediately write new information by overwriting the new information with a write beam. On the other hand, the external magnetic field type needs to write new information with a write beam only after erasing old information with an erase beam.
If such an external magnetic field type optical disk apparatus erases and writes information with a single optical head, a writing action lags behind a reading action, since two rotations of an optical disk are necessary for writing information on a single track.
To solve this problem, an optical disk apparatus with two optical heads, i.e. an optical head for erasing and another for writing, combined into a single optical head system has been developed, so that one track's information can be erased and written in a single rotation of an optical disk.
FIG. 1 is a block diagram of the basic configuration of such an existing optical disk apparatus that can erase and write information.
In FIG. 1, an optical disk 30 is composed of more than one track 31, and information is written into each track 31.
A first optical head 10 is equipped with a first optical system 11 and a first lens actuator 12 inside thereof and read and writes information from and in the optical disk 30.
The first optical system 11 is equipped with a first objective lens 111 and projects a first light beam 112 on the optical disk 30 and generates each light receipt signal for making a first track error signal WTES that indicates a radial difference of the illuminated position of first light beam 112 from the center of the track 31 due to a track oscillation caused by various factors and a first focus error signal WFES that indicates a focus error of the first light beam 112 due to a plane vibration of the optical disk 30.
The first lens actuator 12 performs a focusing control by moving the first objective lens 111 vertically in FIG. 1 according to a first focus drive signal WFDV that is applied from outside and, performs a tracking control by moving the first objective lens 111 horizontally (along the track 31) in FIG. 1 according to a first lens drive signal WLDV that is also applied from outside, thereby causing the first objective lens 111 to follow the track.
The first lens actuator 12 is also equipped with a position sensor inside thereof (not shown in FIG. 1) and generates a light receipt signal for making a first position signal WTPS that indicates the position of the first optical head 10.
A second optical head 20 is equipped with a second optical system 21 and a second lens actuator 22 inside and erases written information in the optical disk 30.
The second optical system 21 is equipped with a second objective lens 211 and projects a second light beam 212 on the optical disk 30 and generates each light receipt signal for making a second track error signal ETES that indicates a radial difference of the illuminated position of second light beam 212 from the center of the track 31 due to a track oscillation caused by various factors and a second focus error signal EFES that indicates a focus error of the second light beam 212 due to a plane vibration of the optical disk 30.
The second lens actuator 22 performs a focusing control by moving the second objective lens 211 vertically in FIG. 1 according to a second focus drive signal EFDV that is applied from outside and performs a tracking control by moving the second objective lens 211 horizontally (along the track 31) in FIG. 1 according to a second lens drive signal ELDV that is also applied from outside.
The second lens actuator 22 is also equipped with a position sensor inside thereof (not shown in FIG. 1) and generates a light receipt signal for making a second position signal ETPS that indicates the position of the optical head 20.
A positioner 40 is equipped with a voice coil motor (abbreviated as VCM) 41, the first optical head 10 and the second optical head 20, and controls the moving of both the optical heads 10 and 20 according to a VCM driving signal VCDV that is applied from outside to the VCM 41.
As shown in FIG. 2A, the first optical head 10 and the second optical head 20 are loaded on the positioner 40 in a configuration such that, when the first light beam 112 of the first optical head 10 illuminates a position on the track 31, the second light beam 21 2 of the second optical head 20 illuminates other position on the same track 31.
A first track servo control part 50 makes the first track error signal WTES and the first track position signal WTPS by a light receipt signal from the first optical system 11 and the first lens actuator 12 and generates, from these WTES and WTPS signals, the first lens driving signal WLDV that controls the moving of the first objective lens 111 to be supplied to the first lens actuator 12. The first track servo control part 50 also generates, from the WTES and WTPS signals, the VCM driving signal VCDV that controls the position of the positioner 40 to be supplied to the VCM 41.
A second track servo control part 60 makes the second track error signal ETES and the second track position signal ETPS by a light receipt signal from the second optical system 21 and the second lens actuator 22 and generates, from these ETES and ETPS signals, the second lens driving signal ELDV that controls the moving of the second objective lens 211 to be supplied to the second lens actuator 22.
A first focus servo control part 80 generates the first focus driving signal WFDV that performs a focus control of the first objective lens 111 by a light receipt signal from the first optical system 11 and supplies WFDV to the first lens actuator 12.
A second focus servo control part 90 generates the second focus driving signal EFDV that performs a focus control of the second objective lens 211 by a light receipt signal from the second optical system 21 and supplies EFDV to the second lens actuator 22.
The above configuration performs a track servo control based on the first optical head 10.
Namely, the first track servo control part 50 makes the first track error signal WTES and the first track position signal WTPS by a light receipt signal from the first optical system 11 and the first lens actuator 12 and generates, from these WTES and WTPS signals, the first lens driving signal WLDV that controls the moving of the first objective lens 111 to be supplied to the first lens actuator 12. The first track servo control part 50 also generates, from the WTES and WTPS signals, the VCM driving signal VCDV that controls the position of the positioner 40 to be supplied to the VCM 41. Thus, the first optical head 10 is controlled, so that the first light beam 112 projected from the first objective lens 111 tracks correctly on the proper track 31 of the optical disk 30.
The first focus servo control part 80 generates the first focus error signal WFES that performs a focus control of the first objective lens 111 by a light receipt signal from the first optical system 11 and supplies WFES to the first lens actuator 12. Thus, the first light beam 112 projected from the first optical head 10 is controlled to focus correctly on the proper track 31 of the optical disk 30.
Meanwhile, as shown in FIG. 2A, the first optical head 10 and the second optical head 20 are loaded on the positioner 40 in such a configuration that, when the first light beam 112 of the first optical head 10 illuminates a position on the track 31, the second light beam 212 of the second optical head 20 illuminates another position on the same track 31. Therefore, in an ideal case where there exists neither any optical head assembling error nor any optical disk eccentricity, when the first optical head 10 is controlled to track correctly on the proper track 31 of the optical disk 30, the second optical head 20 that is to sequentially track on the proper track 31 is controlled to automatically track correctly on the same proper track 31.
When the proper track 31 is tracked on, the second track servo control part 60 performs a track servo control such that the second light beam 212 projected from the second optical head 20 correctly follows the proper track 31 of the optical disk 30.
The second focus servo control part 90 generates the second focus error signal EFES that performs a focus control of the second objective lens 211 by a light receipt signal from the second optical system 21 and supplies EFES to the second lens actuator 22. Thus, the second light beam 212 projected from the second optical head 20 is focus-servo-controlled to focus correctly on the proper track 31 of the optical disk 30.
An existing optical disk apparatus that erases and writes information with two optical heads controls the position of the positioner based on one optical head (a first optical head).
When there exists neither an optical head assembling error nor an optical disk eccentricity, if the reference optical head (the first optical head) is controlled to track correctly on the proper track, the other optical head (the second optical head) can be controlled to track correctly on the same proper track.
However, an actual optical disk apparatus cannot be free from an optical head assembling error. Besides, an optical disk that has a substrate made from plastic materials like PC (Poly Carbonate) and PMMA (Poly Metyl Methacrylate) cannot avoid being warped or externally wavy because of a thermal strain at the time of molding, such as thermal pressurized molding or thermal injection molding. As a result, the surface of the optical disk is inevitably undulated and the track deviates from true roundness. Also, depending on the processing tolerance at the time the center of the optical disk is bored, the center has some eccentricity.
When an optical disk is loaded on a turntable of an optical disk driver, the weight of the optical disk causes a deflection. Thus, an optical disk cannot be free from a built-in vibration of the surface and track, and the optical disk driver also causes such a vibration, because the optical disk driver has a gradient in its turntable and precession.
Therefore, even if the first light beam 112 projected from the first optical head 10 correctly tracks on and follows the proper track 31, the second light beam 212 projected from the second optical head 20 does not track on said proper track 31 and instead follows locations being biased from the center of said track 31, as shown in FIG. 2B. This amount of bias is made generally by superimposing a direct current like bias, such as an assembling error for each optical head, and an alternate current like bias, such as the optical disk eccentricity, and can reach a width as wide as 10 tracks, when the track pitch is 1.6 micro meters, for example.
Consequently, the existing method has a disadvantage in that, when one optical head on which the other one is based correctly tracks on the proper track, the other optical head has only an about 10% chance of tracking on the proper track. Especially when a track jump control or a seek control is made, since the track jump control or the seek control is made based on one optical head, even if the optical head on which the other is based correctly tracks on a proper track, the other optical head has a problem in that it fails to track on the same proper track due to the bias and being prone to track on some other track.